This invention relates to sealing rings for watthour meter mountings and more particularly to a permanent and tamperproof locking arrangement for such sealing rings.
In the field of electric utility metering, watthour meters are universally used for billing a customer's consumption of electric energy. In addition to forming a measuring function, the meters provide a connecting function by being pluggable into a meter socket box. The meter interconnects the customer's electrical wiring and the utility company's distribution power lines. Accordingly, the mounting boxes and meters are usually at open and accessible locations. These locations are necessary to permit installation of the meter mounting box wiring, detachable mounting of the meter and periodic reading of the meter dials. Due to the exposed locations many unauthorized attempts are made at tampering of the meters. Meter tampering often includes removing the meter from the meter socket box and then reattaching with the meter being altered so as to indicate a lower than actual consumption of the electric energy.
Examples of prior art watthour meters having tamperproof or unauthorized alteration preventing features are described in U.S. Pat. Nos. 1,969,499, 3,928,788, 4,034,290 and 4,039,943 all assigned to the assignee of this invention. The aforementioned patents are all directed to permanently sealed watthour meter housings for preventing meter tampering after it has been removed from a meter socket box.
It is desirable to prevent or to provide easy detection of any unauthorized removal of a watthour meter from its socket box. A conventional manner of retaining the meter in the socket box is by a sealing ring which clamps the outer periphery of the meter housing base to the box. After the meter is installed in the socket terminals of the socket box, the sealing ring is contracted by closing the ends, releasably interconnecting the ends, and affixing a frangible wire seal which can be easily broken to release the sealing ring. Often the easily broken wire seal can be replaced and realigned so that only very close examination will reveal that it has been broken, even though it is exposed for inspection to indicate any unauthorized meter removal. An example of a prior art sealing ring is described in the aforementioned U.S. Pat. No. 1,969,499 and further examples are described in U.S. Pat. Nos. 1,893,177 and 2,795,449.
U.S. Pat. Nos. 3,636,498 and 3,996,501 disclose locking arrangements for watthour meters which are mounted in a so-called bottom-connected type of socket box. The meter is mounted so that a clip is installed in locking engagement with a meter housing part and extends inside or behind a meter mounting box enclosure so that the locking clip or tab is inaccessible for removal externally of the box.
An example of providing a locking arrangement for a watthour meter which prevents access to the sealing ring is disclosed in U.S. Pat. No. 3,440,330. In the latter patent, the sealing ring is first applied in a conventional manner and a separate locking plate is mounted over the sealing ring. A further keeper assembly is provided for extending through the locking plate and for receiving a still further padlock device for preventing access and removal of the watthour meter.